A dura mater is a membrane that is present between a brain and a cranial bone and that has the functions of brain protection, cerebrospinal fluid protection and the like. In the craniotomy in the cerebral surgery, a dura mater is necessarily dissected, and it is required to provide a prosthesis for the defect or contract that is thereby caused on the dura mater. For the above prosthesis, conventionally, a human dried dura mater was used. However, the Ministry of Health and Welfare has prohibited the implantation thereof since 1997 for a reason that it may cause the contagion of Creutzfeldt-Jakob disease (CJD).
Artificial dura maters using a stretched fluorine-containing resin (polytetrafuloroethylene) or a silicone resin as a material have been developed as a substitute for the human dried dura mater. Since, however, these plastic materials constituting dura maters are generally in vivo non-degradable polymer materials, it has been reported that they persistently remain in a body to stimulate surrounding tissues chronically and hence cause the thickening of a granulation tissue and internal hemorrhage in the skin.
Further, it has been attempted to produce an artificial dura mater from collagen or gelatin as a main material. However, there is involved a problem that the strength thereof against suturing is deficient and that they cannot retain the membrane strength which is required till the regeneration of a dura mater.
The applicants in JP-A-2003-199817 have proposed an artificial dura mater formed by stacking two or more in vivo degradable synthetic polymer layers. This laminated material has at least one “leakage preventing layer” for preventing the leakage of cerebrospinal fluid from artificial dura mater needle holes. However, the above artificial dura mater has a structure in which two layers having different performances (an elastic layer and a form-retaining layer) are stacked in addition to the above leakage preventing layer, so that the problem with the above artificial dura mater is that its production steps are complicated and that it requires a higher cost.
Artificial dura maters formed of in vivo degradable synthetic polymers, which have been so far proposed, have too high biocompatibility, and there is concern that it may adhere to a brain surface. In a traumatic bran injury in particular, intense bleeding is involved, and the problem with them is that they have a particularly high risk of adhesion. In the above traumatic brain injury, further, the frequency of carrying out the craniotomy again is high. However, when the brain surface and the artificial dura mater should adhere, there is a big problem that makes maneuver of the craniotomy difficult.
Further, Japanese Patent 3,453,648 describes a copolymer that is formed from lactide and glycollide and that has a reduced content of a metal having detrimental effects on organs, and it is described that the copolymer can be applied to an artificial dura mater. However, the above copolymer from lactide and glycollide cannot give any artificial dura mater capable of efficiently preventing the leakage of cerebrospinal fluid, which this invention seeks to provide.
As described above, the present situation is that those artificial dura maters which have been so far proposed cannot necessarily be said to be sufficient in terms of their performances and production processes.
Under the circumstances, it is an object of this invention to overcome the problems of the above prior techniques. For example, this invention seeks to overcome the problems that it is required to stack two layers (an elastic layer and a form-retaining layer) having different performances in addition to the leakage preventing layers in the artificial dura mater disclosed in the above JP-A-2003-199817, that the production cost thereof is high since the production steps on a large-scale thereof are complicated and that it is difficult to render nil the leakage of cerebrospinal fluid from needle holes in the artificial dura meter composed of a stretched fluorine resin or silicone resin as a material.
Further, as a typical method for producing an artificial dura mater, conventionally, a melt-molding method is employed. A lactic acid/glycolic acid/ε-caprolactone copolymer that is a degradable polymer has a problem that it is deteriorated in properties due to a pyrolysis during its melt-molding caused by a remaining metal catalyst used for the polymerization.
It is therefore difficult, by means of the above artificial dura mater, to inhibit the leakage of cerebrospinal fluid for a period required before the regeneration of an autodura mater.
For overcoming the above problems, the present inventors have made diligent studies and as a result arrived at an artificial dura mater that simplifies the production process which could not be accomplished with any conventional artificial dura mater, or that reduces the required number of sheets to be stacked, and that has all of the performances required for an artificial dura mater; (a) it is to have the property showing no leakage which is the function required for an artificial dura mater, in particular it is required to be free of the leakage from needle holes of a suture, said leakage posing a great problem, (b) it is to have a softness close to that of an organic dura mater, (c) it is to be decomposed and absorbed along with the course of tissues repair, (d) it is to be free from adhesion to a brain surface, (e) it is to withstand a suture tension, (f) it is to be free of any deterioration of physical properties during melt-molding, and the like.